Golf club heads come in many different forms and makes, such as wood- or metal-type, iron type (including wedge-type club heads), utility- or specialty-type, and putter-type. Each of these styles has a prescribed function and make-up.
For example, iron-type and utility-type golf club heads generally include a front or striking face, a hosel, and a sole. The front face interfaces with and strikes the golf ball, and may include a plurality of grooves, sometimes referred to as “score lines,” that assist in imparting spin to the ball. The hosel is generally configured to have a particular look to the golfer, to provide a lodging for the golf shaft, and to provide structural rigidity for the club head. Also included is a sole, which is particularly important to a golf shot because it contacts and interacts with the playing surface during the swing.
In conventional sets of iron-type golf clubs, each club includes a shaft with a club head attached to one end and a grip attached to the other end. The club head includes a face for striking a golf ball. The set generally includes irons that are designated number 3 through number 9, and a pitching wedge. One or more additional long irons, such as those designated number 1 or number 2, and wedges, such as a gap wedge, a sand wedge, and a lob wedge, may optionally be included with the set. Alternatively, the set may include irons that are designated number 4 through number 9, a pitching wedge, and a gap wedge.
In golf parlance, the angle between the face and a vertical plane is called the loft angle. Each iron typically has a shaft length that usually decreases through the set as the loft for each club head increases from the long irons to the short irons. Specifically, irons with lower numbers have longer shaft lengths and smaller loft angles. In addition, the overall weight of each club head increases through the set as the shaft length decreases from the long irons to the short irons. To properly ensure that each club has a similar feel or balance during a golf swing, a measurement known as “swingweight” is often used as a criterion to define the club head weight and the shaft length. Because each of the clubs within the set is typically designed to have the same swingweight value for each different lofted club head or given shaft length, the weight of the club head is confined to a particular range.
The length of the shaft, along with the club head loft, moment of inertia, and center of gravity location, impart various performance characteristics to the ball's launch conditions upon impact and dictate the golf ball's launch angle, spin rate, flight trajectory, and the distance the ball will travel. Flight distance generally increases with a decrease in loft angle and an increase in club length. However, difficulty of use also increases with a decrease in loft angle and an increase in club length.
Iron-type golf clubs generally can be divided into three categories: blades and muscle backs, conventional cavity backs, and modern multi-material cavity backs. Blades are traditional clubs with a substantially uniform appearance from the sole to the top line, although there may be some tapering from sole to top line. Similarly, muscle backs are substantially uniform, but have extra material on the back thereof in the form of a rib that can be used to lower the club head center of gravity. A club head with a lower center of gravity than the ball center of gravity facilitates getting the golf ball airborne. Because blade and muscle back designs have a small sweet spot, which is a term that refers to the area of the face that results in a desirable golf shot upon striking a golf ball, these designs are relatively difficult to wield and are typically only used by skilled golfers. However, these designs allow the skilled golfer to work the ball and shape the golf shot as desired.
Cavity backs move some of the club mass to the perimeter of the club by providing a hollow or cavity in the back of the club, opposite the striking face. The perimeter weighting created by the cavity increases the club's moment of inertia, which is a measurement of the club's resistance to torque, for example the torque resulting from an off-center hit. This produces a more forgiving club with a larger sweet spot, which in turn increases the ease of use. The decrease in club head mass resulting from the cavity also allows the size of the club face to be increased, further enlarging the sweet spot. Accordingly, these clubs are easier to hit than blades and muscle backs, and are therefore more readily usable by less-skilled and beginner golfers.
Modern multi-material cavity backs are the latest attempt by golf club designers to make cavity backs more forgiving and easier to hit. Some of these designs replace certain areas of the club head, such as the striking face or sole, with a second material that can be either heavier or lighter than the first material. These designs can also contain undercuts, which stem from the rear cavity, or secondary cavities. By incorporating materials of varying densities or providing cavities and undercuts, mass can be freed up to increase the overall size of the club head, expand the sweet spot, enhance the moment of inertia, and/or optimize the club head center of gravity location.
Traditionally, golf club heads are manufactured to have a certain center of gravity that is not adjustable. However, each individual's swing is as unique as the individual, which results in the fact that one club design will not fit all or even most of today's golfers. For example, a golfer who normally picks the ball clean from the hitting surface would likely prefer a club head with a lower center of gravity allowing for a higher trajectory than a traditional club. On the other hand, a golfer that hits down and through the turf taking a divot would likely prefer a higher center of gravity that allows for a lower trajectory than a traditional club.
In addition, a golfer's swing is likely to vary from day to day based on course conditions, fatigue, and numerous other factors. Due to fatigue, a golfer who normally picks the ball clean may find that he is hitting down on the ball and taking a divot. Further, all golf courses are not identical. For example, on certain courses such as Scottish links, the turf on the fairways is extremely tight and firm. Players are unable to swing down and through the turf, forcing them to sweep or pick the ball clean. In contrast, when windy conditions prevail it is beneficial to have a high center of gravity on the club to keep the ball on a lower trajectory that is less likely to be affected by the wind. Alternatively, on a course with hard, fast greens a golfer is more likely to prefer a lower center of gravity resulting in a higher trajectory and a greater chance of keeping the ball on the green.